Over time, I have gotten confused listening to sales people and tech reps talk about polymers, flocculants, coagulants or precipitants, etc..etc..etc. They seem to interchange the same terms for varying items. Therefore I’ve decided long ago to make up my own mind of what I mean and then let professionals correct me as they see fit. 

 

 

PRECIPITANTS, fall in the realm of chemicals which cause a metal in a dissolved state to become a suspended solid. This includes magnesium hydroxide, sodium hydroxide, DTC among others. They are pH sensitive, and can be adversely affected by compounds such as oxidizers, reducers, oils and other organics. In dealing with batch treatment especially, we have noticed that even low quantities of dissolved grease or oils will stop the precipitation or coagulation process and thus leave dissolved metals in the waste stream. It therefore becomes necessary to break the emulsion of oils and remove them first before trying to precipitate out the metals. The flocs that are developed differ in size but usually are small to medium compared to those formed by coagulants and polymers. 

 

 

COAGULANTS, seem to be a little different in my thinking, in that they tend to grab metallic and nonmetallic substances out of water streams and make small clumps of the target pollutants. The most common are the aluminum based coagulants, or alum. Alum seems to be a somewhat generic term applied to aluminum sulfate, aluminum chloro-hydrate, or poly-aluminum products or PACs. There are many of these and are used not only in the metals removal treatment systems, but also in many other industries as well as drinking water systems. These are quite pH sensitive but not as sensitive to oils and organics. Indeed they are used to remove oils and other emulsions which precipitants cannot. The flocs can range from very small (pin flocs) to large particles the size of big snow flakes. These flocs are very fragile and can break up under high speed mixing. 

 

POLYMERS, (poly-electrolytes). Polymer is used as a term to describe a chemical formed by the union of many monomers (low molecular weight) into a high molecular weight compounds. There are numerous polymers. Some are used in plastics, and other non-wastewater applications.   

 

POLY-ELECTROLYTES are polymers used in wastewater treatment. (Not all polymers are poly-electrolytes). They are produced naturally or are man-made. Natural poly-electrolytes can be of biological origin or derived from starch products or cellulose. Poly-electrolytes or polymers are used to bind with coagulants and precipitants to add weight and mass and help with the removal process.